We have found that tissue transplanted from the optic tectum of fetal rats into the region of the superior colliculus of neonatal rats survives and forms connections with host visual structures. We propose to expand these studies on the superior colliculus and extend them to the visual cortex, using light and electron microscope methods to assess the patterns of connections formed in different circumstances. From this, we hope to be able to define the internal organization of the transplants more carefully and to investigate the questions of special affinities which may exist between particular cell groups within the mammalian visual system. In addition, we plan to grow tissue in tissue culture prior to implantation and using various manipulations, hope to be able to investigate some of the surface properties of the specific connection patterns.